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Materials Science News

This image shows water frozen solid within a carbon nanotube at high temperatures that would normally set it boiling. Image courtesy of the researchers.

Everyone knows that, at sea level, water starts to boil at a temperature of 100°C (212°F). And scientists have long observed that when water is confined in very small spaces, its boiling and freezing points can change a bit, usually dropping by around 10°C or so.

Now, however, a team at Massachusetts Institute of Technology (MIT) has found a completely unexpected set of changes. Inside the tiniest of spaces – in carbon nanotubes whose inner dimensions are not much bigger than a few water molecules – water can freeze solid even at high temperatures that would normally set it boiling.

This discovery illustrates how even very familiar materials can drastically change their behavior when trapped inside structures measured in nanometers, or billionths of a meter. This finding might lead to applications such as ice-filled wires that take advantage of the unique electrical and thermal properties of ice able to remain stable at room temperature. The work is reported in a paper in Nature Nanotechnology by Michael Strano, professor in chemical engineering at MIT, postdoc Kumar Agrawal, and three others.

"If you confine a fluid to a nanocavity, you can actually distort its phase behavior," Strano says, referring to how and when a substance changes between solid, liquid and gas phases. Such distortions in phase behavior were expected for ice in carbon nanotubes, but the enormous magnitude of the change and its direction (raising rather than lowering the freezing point) were a complete surprise.

In one of the team's tests, the water solidified at a temperature of 105°C or more. The exact temperature proved hard to determine, but 105°C was considered the minimum value; the actual temperature could have been as high as 151°C. "The effect is much greater than anyone had anticipated," asserts Strano.

The researchers found that the precise change in the behavior of water inside the tiny carbon nanotubes – structures the shape of a soda straw made entirely of carbon atoms but only a few nanometers in diameter – depends crucially on the exact diameter of the tubes. "These are really the smallest pipes you could think of," Strano says. In the experiments, the nanotubes were left open at both ends, with reservoirs of water at each opening.

Even a tiny difference in the width of the nanotubes (1.05nm vs 1.06nm) produced a difference of tens of degrees in the apparent freezing point, the researchers found. Such extreme differences were completely unexpected. "All bets are off when you get really small," Strano says. "It's really an unexplored space."

In earlier efforts to understand how water and other fluids would behave when confined to such small spaces, "there were some simulations that showed really contradictory results," Strano says. Part of the reason for that is many teams weren't able to measure the exact sizes of their carbon nanotubes so precisely, not realizing that such small differences could produce such different outcomes.

In fact, it's surprising that water can even enter these tiny tubes in the first place. Carbon nanotubes are thought to be hydrophobic, or water-repelling, so water molecules should have a hard time getting inside. Exactly how they’re able to gain entry remains a bit of a mystery, says Strano.

Strano and his team used a highly sensitive analytical technique called vibrational spectroscopy to track the movement of water inside the nanotubes, thus making its behavior subject to detailed measurement for the first time. The team could detect not only the presence of water in the tube, but also its phase.

"We can tell if it's vapor or liquid, and we can tell if it's in a stiff phase," says Strano. While the water definitely goes into a solid phase, the team avoids calling it ‘ice’ because that term implies a certain kind of crystalline structure, which they haven't yet been able to show conclusively exists in these confined spaces. "It's not necessarily ice, but it's an ice-like phase," Strano says.

Because this solid water doesn't melt until well above the normal boiling point of water, it should remain perfectly stable indefinitely under room-temperature conditions. That makes it a potentially useful material for a variety of possible applications. For example, it should be possible to make ‘ice wires’ that would be among the best known carriers of protons, because water conducts protons at least 10 times more readily than typical conductive materials. "This gives us very stable water wires, at room temperature," Strano says.

This story is adapted from material from MIT, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

This image shows how the PSi square GRIN microlens focuses and splits TM- and TE-polarized light, respectively. TM-polarized light is focused at one point while TE-polarized light is focused at two different points. The refractive index gradient for the square microlens under the two different polarizations is illustrated using the color map overlaid on the lens (blue is low refractive index, orange is high refractive index). Image: University of Illinois.

A multi-institutional research team has developed a novel approach to fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi). Reported in a paper in Nano Letters, this work could have broad impacts in integrated optoelectronics, imaging and photovoltaics.

Working with colleagues at Stanford University and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated three-dimensional (3D) birefringent gradient refractive index (GRIN) micro-optics by electrochemically etching preformed silicon micro-structures, like square columns with defined refractive index profiles.

"The emergence and growth of transformation optics over the past decade has revitalized interest in using GRIN optics to control light propagation," explained Paul Braun, professor of materials science and engineering at Illinois. "In this work, we have figured out how to couple the starting shape of the silicon micro-structure and the etch conditions to realize a unique set of desirable optical qualities. For example, these elements exhibit novel polarization-dependent optical functions, including splitting and focusing, expanding the use of porous silicon for a wide range of integrated photonics applications."

"The key is that the optical properties are a function of the etch current," he added. "If you change the etch current, you change the refractive index. We also think that the fact that we can create the structures in silicon is important, as silicon is important for photovoltaic, imaging and integrated optics applications.

"Our demonstration using a 3D, lithographically-defined silicon platform not only displayed the power of GRIN optics, but it also illustrated it in a promising form factor and material for integration within photonic integrated circuits," stated Neil Krueger, a former PhD student in Braun's research group and first author of the paper.

"The real novelty of our work is that we are doing this in a 3D optical element," said Krueger, who recently joined Honeywell Aerospace as a scientist in advanced technology. "This gives added control over the behavior of our structures given that light follows curvilinear optical paths in optically inhomogeneous media such as GRIN elements. The birefringent nature of these structures is an added bonus because coupled birefringent/GRIN effects provide an opportunity for a GRIN element to perform distinct, polarization-selective operations."

According to the researchers, PSi was initially studied due to its visible luminescence at room temperature. More recently, as this and other reports have shown, it has proven to be a versatile optical material, as its nanoscale porosity (and thus refractive index) can be modulated during its electrochemical fabrication.

"The beauty of this 3D fabrication process is that it is fast and scalable," commented Weijun Zhou at Dow. "Large-scale, nanostructured GRIN components can be readily made to enable a variety of new industry applications such as advanced imaging, microscopy and beam shaping."

"Because the etching process enables modulation of the refractive index, this approach makes it possible to decouple the optical performance and the physical shape of the optical element," Braun added. "Thus, for example, a lens can be formed without having to conform to the shape that we think of for a lens, opening up new opportunities in the design of integrated silicon optics."

STRUCTeam Holdings Limited, the holding company of consultancy firm STRUCTeam Limited and software company CompoSIDE Limited, has announced that Paul Peters and David Van Dyke (managing director of Arthur John Capital Limited) have made a strategic investment in the company and have joined the company’s board of directors.

The investment provides a boost to the growth plans of both companies, they say. Peters has experience building and managing a large FinTech company while Van Dyke bring strategic advisory and financial experience in addition to synergies with other investee companies.

‘I am pleased to welcome both David and Paul to the Board of Directors,’ said Julien Sellier, managing director of STRUCTeam Holdings. Their experience will add great value in a number of areas across both STRUCTeam and CompoSIDE, as both companies continue to grow. The addition that these new appointments will make to the group will contribute to our continued success.’

This story is reprinted from material from CompoSIDE, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.

Resin supplier AOC has been named Gold Supplier of the Year by Bombardier Recreational Products (BRP), which makes motorized recreational vehicles. The award recognizes supply chain partners who demonstrate performance in quality, service and costs. AOC supplies BRP’s SEA-DOO division in Mexico where they produce up to 175 SEA-DOO hulls a day.

BRP said that AOC achieved 100% on-time delivery, zero returns and provided invaluable technical support with closed mold and open mold processes.

This story is reprinted from material from AOC, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.

Linde AG says that it has decided to resume talks over the essential terms of a potential merger of equals between it and Praxair Inc. All members of the supervisory board support resuming the talks.

At the same time Dr Wolfgang Büchele, CEO of Linde, has offered to the Supervisory Board that he resigns his mandate, effective from the end of today. Thus, continuity for the forthcoming negotiations is ensured. The supervisory board has accepted this request and appointed Professor Dr Aldo Belloni to succeed him as CEO.

Belloni, who served on the executive board of Linde from 2000 to 2014, will take up office on 8 December. His appointment runs to the end of 2018.

‘With the resumption of the talks, a successful merger is now drawing near,’ said Dr Büchele. ‘I have already set a course for my own future and with this step I am acting in the best interest of the company. With a succession plan in place, the necessary continuity is assured without interruption for the demanding tasks of the coming months. I am very pleased that, with the resumption of the merger talks, Linde's leading global role is close at hand.’

‘On behalf of the Supervisory Board, but also on my own personal behalf, I would like to thank Wolfgang Büchele for everything he has contributed to our company and for his trusting working partnership,’ said Professor Dr Wolfgang Reitzle, chairman of the supervisory board. ‘Wolfgang Büchele took on the role of chief executive officer in economically and structurally challenging times. We are therefore all the more thankful for his introduction of initiatives to secure and extend Linde's leading role in the global marketplace.’

This story is reprinted from material from Linde, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.

Dr Camila Fernandez has received the €10,000 Umicore Materials Technology Award for her PhD work in the field of exploring dynamic catalytic processes for synthesizing ammonia on ruthenium-supported nanoparticles at low temperatures.

Dr Fernandez's entry was one of 15 submitted from all over Europe.

Dr Fernandez, who is from Chile, started her academic work on catalysis during her masters studies at the University of Concepción in that country. During these studies, she took part in a research exchange at UCL where she deepened her interest in the subject. In 2011, she moved to Belgium to embark on her doctoral studies under the supervision of Professors Eric Gaigneaux and Patricio Ruiz at UCL's Institut de la Matière Condensée et Nanosciences.

‘I am very happy that this work has been recognized in the industrial world,’ said Dr Fernandez. ‘The research that we have done sheds new light on the way catalytic reactions work and will hopefully lead to further improvements in catalytic performance in the future.’

‘Catalysis is one of Umicore's main competences and we hope that Dr Fernandez's work will increase awareness and understanding of catalysis in this specific field,’ said An Van de Vel, Umicore's senior manager of external science and technology. ‘Her thesis is also an example of outstanding academic work that has obvious practical benefits such as lowering energy consumption and increasing selectivity in catalytic reactions.’

The most prestigious prize for PhD students in chemistry recognising young chemists’ work will open for submissions on 9 January 2017. Now in its eighth year, the Reaxys PhD Prize has attracted thousands of entries from over 400 academics institutions worldwide.

The Prize is open to PhD students who have just published (or are about to) a peer-reviewed paper in chemistry (or are about to). Watch the video here.

Each year, 45 finalists are selected from the submissions and invited to present their research at the Symposium. They will also join the Reaxys Prize Club, an exclusive community composed by the finalists of the previous years. The 3 winners, chosen during the Symposium, will each win $2000.

UK composites manufacturer Tufcot says that it has had one of its most successful months of the year in November. As a result, the company is now back to 24 hour production operations over the next few weeks.

Products being ordered in November include long tubes, high volume split rings, and large bearings with external grooves and holes.

This week will be the last week Tufcot are scheduling any finished products to be shipped in 2016. Raw material tubes and laminates will still be shipped in either week 49 or week 50, the company says.

This story is reprinted from material from Tufcot, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.

Evonik Resource Efficiency plans to invest in a capacity expansion of its performance foams business at its production site in Darmstadt, Germany. The investment is said to initially increase the output of the facility by about 20%.

The Darmstadt plant is currently producing Rohacell foam products as a core material in the construction of sandwich composites. Rohacell is a rigid, lightweight structural polymethacrylimide foam used in the design and production of sandwich composites in aerospace, automotive, marine, sports equipment, electronics and medical technology. The global market has shown steady annual growth in the use of composites as multiple industries are facing the challenge of producing products for their customers that are lighter in weight, strong and dependable, the company says.

Evonik will also be adding production equipment to its operations complex that manufactures products marketed under the Rohacell brand. The expanded production capacity is expected to be operational by the second half of 2017.

‘We have experienced double-digit growth of the Rohacell brand in recent years and have indications that this success will continue,’ said Dr Matthias Kottenhahn, senior vice president of High Performance Polymers Business Line at Evonik Resource Efficiency Segment.

‘As the trend toward composite usage continues, we are prepared to respond with the lightweight solutions available in our Rohacell range of foam products,’ added Dr Andreas Hoff, vice president of performance foams. ‘Whether it is an airplane, a car, a ship, a wind turbine blade, an electronic device or even a hockey stick – all can benefit from less overall weight.’

This story is reprinted from material from Evonik, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.

Single layer sheets of graphene have been synthesised at the company's industrial processing facilities in the UK.

Metalysis Ltd reports that it has successfully produced graphene using the company’s proprietary electrochemical metal powder manufacturing process.

Single layer sheets of graphene have been synthesised at the company's industrial processing facilities in the UK, as well as bilayer and low multi-layer amalgamations. Now the company plans to focus on differentiating and separating the single atom width sheets.

Graphene is super strong, lightweight and highly conductive, exhibiting metallic-like properties in 2D form. It could revolutionise a host of future applications across a wide range of sectors such as light materials (aerospace and automotive), semiconductors, energy electrodes, nanotechnology and printable inks.

While graphene is traditionally known to incur high costs of production, Metalysis says that it is able to produce the largely industrially inaccessible material at no additional production cost to its conventional operations. The company is now focused on further process optimization and plans to pursue commercial opportunities during the coming year.

Lucrative markets

‘We are pleased to announce another exciting achievement on behalf of our technical team,’ said
Dr Dion Vaughan, CEO of Metalysis. ‘Our proven technology can synthesise graphene monolayers with no operational or production cost impacts on our core metal powder business.

‘Producing graphene could enable Metalysis to add new, lucrative markets to those it is already serving; markets in which our arrival could be highly disruptive when global product demand is considered against the sheer amount of graphene we could produce in conjunction with our Gen 4, and later Gen 5 modular expansions. Gen 5, by way of illustration, envisages scaling up production capability for highly profitable niche multi-metal powders to thousands of tonnes per annum.’

This story is reprinted from material from Metalysis, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.

The textile industry relies on organic dyes but they are damaging to the environment if discharged, toxic, and non-biodegradable. Before wastewater from textile production plants can be released, treatment to remove organic dyes is essential. Current approaches mostly rely on filtration and absorption, but this creates further – secondary – waste that also has to be treated.

As an alternative, scientists are looking for ways to break up organic dyes into smaller, harmless molecules. These so-called degradation reactions require light-activated catalysts to drive the process. Semiconducting materials, particularly TiO2, have attracted interest as potential photocatalysts because of their high stability and activity combined with low cost and toxicity.

A simple photocatalytic system based on TiO2 nanoparticles grown on quartz beads could be the answer, according to Ruitao Zhou of the Hong Kong Polytechnic University in China and M. P. Srinivasan of RMIT University in Australia, because it provides a large surface area for reactions to occur, long-term durability, and is self-cleaning.

“We invented this technique to avoid the disadvantages of common nanoparticles in catalysis, such as aggregation, blocking by surfactants, difficulties with recycling, and scalability,” explains Zhou.

The TiO2 nanoparticles that form on the surface of the quartz beads have a crystalline core/disordered shell structure. A thin film of the functional polymer 4-methoxycalix arene sticks the nanoparticles onto the quartz surface ensuring that they do not bunch together or become blocked by the organic molecules.

The treatment system itself consists of a quartz tube filled with the nanoparticle-covered beads. To demonstrate its capabilities, an organic dye – in this case methyl orange (MO) – was fed into the glass tube. When exposed to visible or UV light, electron-hole pairs generated by the TiO2 nanoparticles produce radicals (OH•), which break up the dye molecules into smaller species.

Zhou and Srinivasan’s photocatalytic setup successfully treated a continuous flow of MO over 140 hours, with activity only showing the first signs of decrease after 120 hours. Moreover, a simple rinse through with de-ionized water for an hour rejuvenates the treatment system.

“The TiO2 nanoparticles could be used for treating water polluted with organic waste,” says Zhou. “Compared with existing approaches, this system can treat polluted water in situ because no secondary waste is generated.”

The researchers believe the approach could be easily scaled up and could be applied to the fabrication of other nanostructures.

This image shows theoretical (right) and experimental (left) iso-frequency contours of photonic crystal slabs superimposed on each other. Image courtesy of the researchers.

Researchers at Massachusetts Institute of Technology (MIT) have developed a new technique for revealing the inner details of photonic crystals, synthetic materials whose exotic optical properties are the subject of widespread research.

Photonic crystals are generally made using microchip fabrication methods to drill millions of closely-spaced, minuscule holes in a slab of transparent material. Depending on the exact orientation, size and spacing of these holes, photonic crystals can exhibit a variety of peculiar optical properties. These include ‘superlensing’, which allows for magnification that pushes beyond the normal theoretical limits, and ‘negative refraction’, in which light is bent in an opposite direction to its normal path through transparent materials.

But understanding exactly how light of various colors from various directions moves through photonic crystals requires extremely complex calculations. Because of this, researchers often use highly simplified approaches; for example, they may only calculate the behavior of light along a single direction or for a single color.

The new technique developed by the MIT researchers makes the full range of information directly visible in the form of a pattern of so-called ‘iso-frequency contours’ that can be photographed and examined. In many cases, these contours eliminate the need for any calculations. The technique is detailed in a paper in Science Advancesby MIT postdoc Bo Zhen, recent Wellesley College graduate and MIT affiliate Emma Regan, MIT professors of physics Marin Soljacic and John Joannopoulos, and four others.

The discovery of this new technique, Zhen explains, came about by looking closely at a phenomenon that the researchers had noticed and even made use of for years, but whose origins they hadn't previously understood. Patterns of scattered light seemed to fan out from samples of photonic materials when the samples were illuminated by laser light. The scattering was a surprise, since the underlying crystalline structure of these materials was fabricated to be almost perfect.

"When we would try to do a lasing measurement, we would always see this pattern," Zhen recalls. "We saw this shape, but we didn't know what was happening." The pattern did at least prove useful in helping to get their experimental setup properly aligned, because the scattered light pattern would appear as soon as the laser beam was properly lined up with the crystal. Upon careful analysis, however, the researchers realized the scattering patterns were generated by tiny defects in the crystal – holes that were not perfectly round in shape or that were slightly tapered from one end to the other.

"There is fabrication disorder even in the best samples that can be made," Regan explains. "People think that the scattering would be very weak, because the sample is nearly perfect." At certain angles and frequencies, however, the light scatters very strongly: as much as 50% of the incoming light can be scattered. By illuminating the sample in turn with a sequence of different colors, it becomes possible to build up a full display of the relative paths taken by the light beams, all across the visible spectrum. The scattered light produces a direct view of the iso-frequency contours – a sort of topographic map of the way light beams of different colors bend as they pass through the photonic crystal.

"This is a very beautiful, very direct way to observe the iso-frequency contours," Soljacic says. "You just shine light at the sample, with the right direction and frequency," and what comes out is a direct image of the needed information, he says.

This finding could potentially prove useful in a number of different applications, the team says. For example, it could lead to a way of making large, transparent display screens where most light would pass straight through, as if through a window, but light at specific frequencies would be scattered to produce a clear image on the screen. Or the method could be used to make private displays that would only be visible to the person directly in front of the screen.

Because it relies on imperfections in the fabrication of the crystal, this method could also be used as a quality-control measure for the manufacture of such materials. The images not only provide an indication of the total amount of imperfections, but also of their specific nature – that is, whether the dominant disorder in the sample comes from noncircular holes or etches that aren't straight – allowing the manufacturing process to be tuned and improved.

This story is adapted from material from MIT, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

New features are being offered on a range of ribbon blenders, which are used for rapid blending of dry powders, granules, pellets and other solid forms.

The blenders, supplied by mixer specialist Charles Ross, can also mix paste-like materials and solid-liquid suspensions. Materials are blended by a horizontal agitator consisting of inner and outer helical ribbons within a U-shaped trough. The ribbons are pitched to move materials in a well-balanced axial and radial flow pattern.

Charles Ross says that model 42N-120SS, is now equipped with a solid agitator shaft with ribbons having angled leading edges to prevent material build-up, scrapers welded to the spokes and ribbons, having a close tolerance (1/8’) to the end walls and clear view polycarbonate on the cover and shaft guards. The cover can also include ports for ingredient additions, lights, spray system, venting and vacuum transfer.

This story is reprinted from material from Charles Ross, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.

Experts from the automotive and manufacturing technology industries attended at a workshop at GKN.

Experts from the automotive and manufacturing technology industries have attended at a workshop at GKN to learn more about the new possibilities of metal additive manufacturing (AM) in series production, the company reports.

‘There is no stopping the advancement of metal AM,’ said Ümit Aydin, global BD additive manufacturing. ‘We all agree on this future technology’s huge potential. ‘But on the threshold of series production, we must carefully consider the pros and cons in each and every case.’

The workshop highlighted both the technical and commercial aspects of possible AM manufacturing and made use of the company’s MetalFAB1, AM machine that can enable series production parts for engines and transmissions.

GKN Sinter Metal’s next AM workshop is planned for the first quarter of 2017.

This story is reprinted from material from GKN, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.

Automotive giant SKF reports that it has participated in three simultaneous raids against retailers of counterfeit bearings in China. The raids, which were led by Chinese police, resulted in the seizure of counterfeit bearings which may otherwise have been sold to industrial customers and end-users.

‘Counterfeit products are often associated with luxury and consumer brands, but they are also a problem for industrial customers in almost all regions,’ said Tina Astrom, director, group brand protection. ‘Although the sale of counterfeit bearings is a problem in China, Chinese law enforcement is very proactive and supported by a legal framework that enables taking action against counterfeiters.

‘Amongst the seized goods, there was a counterfeit large-size cylindrical roller bearing. The bearing had severe visible damage, suggesting that it had not been able to meet the performance needs of the machine in which it was installed. The damage was so severe, the failure of the counterfeit bearing would most likely have created substantial damage to its surrounding machinery, resulting in unplanned production downtime and financial implications for the end-user.’

This story is reprinted from material from SKF, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.

Produced from computer simulations, this image shows the response of a graphene surface as a silicon tip slides over it. Relative forces of atomic friction on the surface are shown by colors: red points are pushing sites that help propel the tip along the surface, while blue points are pinning sites of greater friction that inhibit the tips motion. Image courtesy of the researchers.

Graphene, a two-dimensional (2D) form of carbon comprising layers just one atom in thick, has been the subject of widespread research, in large part because of its unique combination of strength, electrical conductivity and chemical stability. But despite many years of study, some of graphene's fundamental properties are still not well understood, including the way it behaves when something slides along its surface.

Now, using powerful computer simulations, researchers at Massachusetts of Technology (MIT) and elsewhere have made significant strides in understanding that process. This includes determining why the friction varies as an object slides across graphene, instead of remaining constant as it does with most other known materials.

The findings appear in a paper in Nature by Ju Li, professor of nuclear science and engineering and of materials science and engineering at MIT, and seven other researchers at MIT, the University of Pennsylvania, and universities in China and Germany.

Graphite, a bulk material composed of many layers of graphene, is a well-known solid lubricant (just like oil, it can be added between contacting materials to reduce friction). Recent research suggests that even one or a few layers of graphene can also provide effective lubrication, which could prove of use in small-scale thermal and electrical contacts and other nanoscale devices.

In such applications, an understanding of the friction between two pieces of graphene, or between graphene and another material, is important for maintaining a good electrical, thermal and mechanical connection. Researchers had previously found that while one layer of graphene on a surface reduces friction, having a few more was even better. However, the reason for this was not well understood.

"There is this broad notion in tribology that friction depends on the true contact area," Li says – that is, the area where two materials are really in contact, down to the atomic level. The ‘true’ contact area is often substantially smaller than it appears to be if observed at larger scales. Determining the true contact area is important for understanding not only the degree of friction between materials, but also other characteristics such as electrical conduction and heat transfer.

For example, explains co-author Robert Carpick of the University of Pennsylvania: "When two parts in a machine make contact, like two teeth of steel gears, the actual amount of steel in contact is much smaller than it appears, because the gear teeth are rough, and contact only occurs at the topmost protruding points on the surfaces. If the surfaces were polished to be flatter so that twice as much area was in contact, the friction would then be twice as high. In other words, the friction force doubles if the true area of direct contact doubles."

It turns out, however, that the situation is even more complex than originally thought. Li and his colleagues found that other aspects of the contact also influence how the friction force gets transferred across it. "We call this the quality of contact, as opposed to the quantity of contact measured by the 'true contact' area," Li explains.

Experimental observations had shown that when a nanoscale object slides along a single layer of graphene, the friction force actually increases at first, before eventually leveling off. This effect lessens, and the leveled-off friction force decreases, when sliding on more and more graphene sheets. This phenomenon has also been seen in other layered materials including molybdenum disulfide. Previous attempts to explain this variation in friction, not seen in anything other than these 2D materials, had fallen short.

To determine the quality of contact, it is necessary to know the exact position of each atom on each of the two surfaces. The quality of contact depends on how well-aligned the atomic configurations are in the two surfaces in contact, and on the synchrony of these alignments. According to the computer simulations, these factors turned out to be more important than the ‘true’ contact area in explaining the materials' frictional behavior.

"You cannot explain the increase in friction" as the material begins to slide "by just the contact area," Li says. "Most of the change in friction is actually due to change in the quality of contact, not the true contact area." The researchers found that the act of sliding causes graphene atoms to make better contact with the object sliding along it; this increase in the quality of contact leads to an increase in friction as sliding proceeds, before the friction eventually levels off. The effect is strong for a single layer of graphene because it is so flexible that the atoms can move to locations of better contact.

A number of factors can affect the quality of contact, including the rigidity of the surfaces, slight curvatures and gas molecules that get in between the two solid layers, Li says. But by understanding the way the process works, engineers can now take specific steps to modify the frictional behavior of graphene to match a particular intended use. For example, ‘prewrinkling’ of the graphene material can give it more flexibility and improve the quality of contact. "We can use that to vary the friction by a factor of three, while the true contact area barely changes," he states.

"In other words, it's not just the material itself" that determines how it slides, but also its boundary condition – including whether it is loose and wrinkled or flat and taut, Li explains. And these principles apply not just to graphene but also to other 2D materials, such as molybdenum disulfide, boron nitride, and other single-atom or single-molecule-thick materials.

"Potentially, a moving mechanical contact could be used as a way to make very good power switches in small electronic devices," Li says. But that is still some way off; while graphene is a promising material being widely studied, "we're still waiting to see graphene electronics and 2D electronics take off. It's an emerging field."

This story is adapted from material from MIT, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

A typical CH3NH3(Mn:Pb)I3 perovskite crystal developed by the EPFL researchers. Photo: László Forró/EPFL.

Scientists at Ecole Polytechnique Fédérale de Lausanne (EPFL) in France have developed a new perovskite material with unique properties that could be used to build next-generation hard drives.

Storage systems, e.g. hard drives, with higher density and efficiency are required to store the ever greater volumes of data being generated. Such systems require materials whose magnetic properties can be quickly and easily manipulated in order to write and access data on them. EPFL scientists have now developed a perovskite material with a magnetic order that can be rapidly changed without any excess heating. A paper on this work, describing the first ever magnetic photoconductor, appears in Nature Communications.

In the lab of Laszló Forró at EPFL, postdoc Bálint Náfrádi synthesized a ferromagnetic photovoltaic material comprising methylammonium, manganese, lead and iodine (CH3NH3(Mn:Pb)I3). Perovskite photovoltaics are becoming a cheaper alternative to current silicon solar cells, drawing much interest from energy scientists. But the specific perovskite synthesized by Náfrádi exhibits some unique properties that make it particularly interesting as a material for use in next-generation digital storage systems.

Magnetism arises from the interactions between localized and moving electrons in a material, and can be viewed as the result of competition between the different movements of these electrons. This means that the resulting magnetic state is hard-wired in the material and cannot be reversed without changing the material's chemistry or crystal structure. Having an easier way to modify magnetic properties would, however, be incredibly useful for applications such as magnetic data storage.

The new material developed by EPFL scientists provides just such an easier way. "We have essentially discovered the first magnetic photoconductor," says Náfrádi. The crystal structure of the new perovskite combines the advantages of both ferromagnets, whose magnetic moments are aligned in a well-defined order, and photoconductors, where light illumination generates high density free conduction electrons.

Combining these two properties produced an entirely new phenomenon: the ‘melting’ of magnetization by photoelectrons, which are electrons emitted from a material when irradiated with light. In the new perovskite material, a simple red light-emitting diode (LED) – much weaker than a laser pointer – is sufficient to disrupt, or ‘melt’, the material's magnetic order and generate a high density of traveling electrons. These electrons can be freely and continuously tuned by altering the light's intensity. The timescale for shifting the magnetic order in this material is also very fast, just quadrillionths of a second.

Although still at the experimental stage, with these properties the new material could be used to build the next generation of memory-storage systems, featuring higher capacities with low energy demands. "This study provides the basis for the development of a new generation of magneto-optical data storage devices," says Náfrádi. "These would combine the advantages of magnetic storage – long-term stability, high data density, non-volatile operation and rewriteability – with the speed of optical writing and reading."

This story is adapted from material from EPFL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

The recipient of the 2017 Acta Biomaterialia Gold Medal is Professor Allan S. Hoffman, Emeritus Professor of Bioengineering at the University of Washington in Seattle. The Award will be presented at the 2017 Meeting of the Society for Biomaterials to be held in Minneapolis in April 2017.

Professor Hoffman studied at M.I.T., where he received his B.S., M.S., and Sc.D. degrees in Chemical Engineering between 1953 and 1957. He taught on the faculty of the Chemical Engineering Department at M.I.T. for a total of ten years. He then spent 46 years as Professor of Bioengineering and Chemical Engineering at the University of Washington in Seattle, Washington.

Prof. Hoffman’s major research interests are in drug delivery; diagnostic assays; “smart”, stimuli-responsive polymers; hydrogels; and chemical and biological modification of biomaterial surfaces. He has published over 400 peer-reviewed articles and is co-inventor on over 35 issued patents. He is co-Editor (along with Buddy D. Ratner, Fred J. Schoen and Jack E. Lemons) of the “Textbook of Biomaterials Science”, Elsevier Publishers, now in its 3rd Edition.

His early work in 1984 on the use of “smart” polymers in a temperature-driven phase separation immunoassay sparked a huge worldwide interest in such stimuli-responsive polymers as biomaterials. Biomedical applications of “smart” polymers continue to grow rapidly around the world at the present time.

He has been an Honorary Professor at: Sichuan University, Chengdu, China; South China University of Technology, Guangzhou, China; Wuhan University, Wuhan, China; Shanghai University, Shanghai, China; and Aarhus University, Aarhus, Denmark. In 2013 he completed a four-year appointment (2009-2013) as WCU (“World Class University”) Distinguished Professor at the Kyungpook National University Medical School in Daegu, South Korea.

Professor Hoffman was elected to the US National Academy of Engineering in 2005. His other recognitions and awards include Presidency of the US Society for Biomaterials (1983); the “Biomaterials Science Prize” of the Japanese Society for Biomaterials (1990); the Founders’ Award of the US Society for Biomaterials (in 2000); the Chandra Sharma Award of the Society for Biomaterials and Artificial Organs of India (2003); the “International Polymer Research Award” of the Japanese Society of Polymer Science (2006), and the Founder’s Award of the US Controlled Release Society (2007);

Special symposia have been organized in Maui, Hawaii by his colleagues to celebrate his 60th, 70th and 80th birthdays. Former students, along with many academic colleagues, have also organized symposia which they have called “Hoffman Family Symposia” (HFS) and since 2010 there have been four, the first two were in Tokyo, Japan in 2012 and 2014, the third was in Gwangju, Korea in 2015, and a fourth was in Taipei, Taiwan September, 2016. A fifth HFS will be held in Shanghai, China this coming October, 2017.

North Thin Ply Technology (NTPT) says that its ThinPreg 736LT prepreg system has now been approved by Lloyd’s Register.

NTPT’s composite technology is suitable for the marine market and this latest certification confirms the company’s continued commitment to development in this sector, the company says.

The prepreg system has been formulated to offer long out life (up to 8 weeks at 18-22°C) and has improved mechanical performance. The system can be used in the production of large structures and can be cured at temperatures as low as 80°C.

ThinPreg 736LT UD prepregs can be supplied in a full range of weights from 30 gsm upwards and in plotted multiaxial formats such as a 400g +/-45° available in widths up to 4m.

NTPT also offers a compatible set of 736LT products such as prepreg peel ply, woven fabrics and adhesive films for core bonding.

This story is reprinted from material from NTPT, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.

The finished composite façade on the new Eurojust office building in The Hague, Netherlands.

Resin supplier Aliancys has helped develop a composite façade solution for the construction of the new Eurojust office building in The Hague, Netherlands.

The project, which required the delivery of over 700 façade panels of multiple widths and lengths ranging from 3.5 to 10 m was specified by TGM, a Dutch construction company specialized in the installation of building façade systems.

This façade assembly also includes structural components, insulation to heat and moisture, ingress protection, as well as elements that provide aesthetics.

The composite components were made by component manufacturer Indupol through a hand lay-up process in modular molds that were adjusted to the desired shape and dimensions, using resin from Aliancys and Büfa (delivered through Distributor Euroresins). After molding, the parts were treated with a topcoat in white color and transported to the job site for installation.

‘We have learned that involving all relevant players in the supply chain right from the start was the key to success, enabling to truly combine the technical expertise from different companies,’ said Leon van Osch, general manager of TGM. ‘In this project we have been under continuous time pressure to develop a cost-effective façade system that could meet a long list of requirements. In such a process open communication is crucial, as during design and production scale-up unexpected situations will arise by definition and need to be tackled in a smooth way. We believe that composite façade systems have a promising future, based on the success we created with our partners in this great project.’

This story is reprinted from material from Aliancys, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.